GB1359471A - High temperature process for thermoplastic filaments and films - Google Patents

Abstract

1359471 Porous filaments RADUNER & CO AG 2 July 1971 [22 July 1970] 35559/70 Heading B5B [Also in Division C3] Melt-spun filaments or melt extruded films containing voids, vacuities, surface indentations and cracks having a total surface area (the total area on the inside and outside of the filament which is accessible to low molecular weight gases and liquids) which is at least three times (preferably at least 10 times) their average surface area as determined by multiplying the average circumference of the filaments by their length are prepared by a process which involves heating thermoplastic polymer filaments or films at a temperature at least 100‹ C. above the glass transition temperature of the polymer and cooling the heated material, the temperature and time of heating being such that the peripheral portions of the filaments or films are affected to a larger degree than the inner portions, thereby creating a temperature gradient across the material cross-section. Preferably the material is heated to a temperature at least 150‹ C. above its glass transition temperature; the time of heating is less than 15 sees. when the temperature of heating is near or above the softening point of the thermoplastic polymer and less than 1 sec. when the temperature is near or above the melting point of the polymer; and the filament is stretched by at least 5% its elongation at break during or after cooling. The filament may contain a liquid, gaseous or solid pore-forming agent which is preferably a swelling agent for the thermoplastic polymer and is applied prior to heating. Heating may be effected by infra-red, lasers, microwave, or with a liquid, gaseous or solid (fluidized bed) heating medium. In examples nylon 6 or 6 : 6 filaments are swollen in water, polyethylene glycol, dimethyl sulphoxide, moist air or ethanol, heated in ethylene glycol, paraffin oil, cetyl alcohol vapour, a fluidized sand bed or by infra-red for a time from 0À3 to 22 seconds at a temperature between 205 and 301‹ C. and are then cooled rapidly. In Example 9 a nylon 6 : 6 filament is cooled to - 60‹ C. in solid CO 2 and then rapidly heated for 0À3 secs. at 257‹ C. Example 10 relates to the production of a porous polyethylene terephthalate filament using cone. HCl as swelling/pore-forming agent and a heat treatment time of 3 seconds at 245‹ C.